The ability to detect seal patterns in an image can be useful in copier machines or scanners for the purpose of authenticating documents or preventing counterfeiting. The challenge of incorporating such a method in current copier or scanning technology is the difficulty with detecting seals patterns in a rotation or shift invariant manner. Specifically, the pattern could be of any orientation and at any location of the image. The orientation and the location of the seal can be relatively simple to estimate in the case of a single seal within a plain background; however, it becomes a major obstacle when the seals are embedded in some complicated image background.
Prior anti-counterfeiting or pattern detection methods are presented by the following patents: